As wear-resistant materials comprising superabrasive particles, diamond or cubic boron nitride compacts are commercially produced mainly in ultrahigh pressure processes, and in which the superabrasive particles are joined immediately with each other or distributed in a ceramic matrix. While the compacts may be employed as a block of totally uniform structure, they are more commonly used as a composite with a carbide backing to which the superabrasive particles are joined during the sintering of the particles themselves. The latter composition is taken mainly as demanded in the subsequent steps of machining into the final shape or brazing to the support, where a less superabrasive thickness is favored for a higher efficiency, or a such backing facilitates the work.
However carbide alloy, being a hard and brittle material, cannot fully comply with the residual stresses which occur at the carbide and superabrasive interface after cooled down due to the difference in thermal expansion coefficient. They may eventually cause to disjoint the layers at a slightest external load.
Further, the use of carbide alloy is not advantageous for the rather high material cost and high specific gravity.
It is known to use a self-propagating high-temperature synthesis (SHS) for the preparation of some types of functional materials. The technique is based on the process which occurs with appropriate material systems: a combustion, once initiated by igniting at a spot, sustains itself and propagates throughout the rest of the material, due to an intense production of heat which spreads and causes a sufficient temperature rise. It is useful for the production of such compounds as, for example, carbide, nitride, boride, silicide or oxide of the fourth or fifth group metals of the periodic table, including Ti, Zr, Ta, Si, as well as intermetallic compounds. This technique is fully described in "The chemistry of SHS", published by T.I.C. (1992).
An SHS process, which can produce high temperatures over a short period of time almost adiabatically, is employed for the formation and sintering, simultaneous or subsequent, of high melting materials and, if tentatively, for the preparation of compact of various materials. For the materials, these techniques are available: static compression with a mechanical press, instantaneous compression by explosive detonation, isostatic compression with a HIP system, quasi HIP process whereby the formed compact is squeezed from around with a mechanical press in a die by means of molding sand.
One of the principal objects of the present invention is to eliminate the above described problems which are associated with conventional processes and products involving an ultrahigh pressure technique, and thereby to provide a heat-resistant product, and also a method for effectively producing the same, which comprises a metallic layer improved both in mechanical material strength and thermal stability of the joint strength to the ceramic substrate. This has been achieved effectively on the basis of an SHS technique.
This is an advanced variation of our previous applied invention which is based on a combined process of SHS with compression and in which metallic ingredients are molten with the intense heat of an SHS reaction and allowed to penetrate the skeletal structure of in situ formed ceramic material, so that the gaps within and among it are filled in. The product of compact structure exhibits a high resistance to both heat and abrasion that conventional techniques could not achieve.